Poole has only been eligible to play for his new club for a month but made his debut on Thursday.Getty

Cardiff City manager Russell Slade admits the club made a huge mistake in allowing Manchester United starlet Regan Poole to leave the club. Poole, 17, joined United from Newport County on the final day of the summer transfer window having made just 17 appearances for the League Two club.

The Welsh defender had previously been part of the Cardiff academy but was released in 2012. While Slade didn't take over at the Bluebirds in 2014, he feels the club should have done more to keep hold of the promising youngster.

"You don't want to be losing that type of quality," Slade was quoted as saying by BBC Sport. "Occasionally one does get away because young players develop at different rates. But clearly a decision was made at the particular time and they got it wrong.

"I cannot control what has happened in the past, before my time. But certainly, if I had been here as manager at the time – obviously the personnel has changed at that level since then as well – you would be wanting to know the reasons why."

Poole made his United debut in the 5-1 victory over Midtjylland on Thursday 26 February, replacing Ander Herrera during injury time. After his reported £100,000 ($145,000) move to Old Trafford in September, he had been unable to make his competitive debut for the club – including games for the Under-21 side – due to a delay regarding his international clearance, as reported by the South Wales Argus.

That stand-off continues until just last month when Poole was cleared to play for Warren Joyce's Under-21 side.

Former Manchester United and Wales international Mickey Thomas has already tipped the youngster to go on and become a regular for his country.

"It's a big step for the youngster, obviously coming from Newport County, but to make the first-team debut - it makes no difference if it's for a minute or 10 seconds - he's actually made a first-team debut now and he'll be an excited young boy.

"But he knows there's a long way to go in his career, but it's the first step and it's a massive step to make his debut at Old Trafford."